What sprocket gearing - Wrist Twisters
 
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post #1 of 20 Old 07-21-2018, 06:51 AM Thread Starter
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What sprocket gearing

Hey guys i have been drag racing allot this summer just for the fun of it anf i have been really surprised by the cb919 at the drag strip. Im due for chain and sprocket and was wondering what gearing i should get for better times. Should i stay with the stock gearing or go up a tooth in the front or down. Should i go say 15-43 or 16-44 or maybe 17-44 i dont know, i still want it to be rideable

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post #2 of 20 Old 07-21-2018, 09:34 AM
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Quote:
Originally Posted by Nikolav1990 View Post
Hey guys i have been drag racing allot this summer just for the fun of it anf i have been really surprised by the cb919 at the drag strip. Im due for chain and sprocket and was wondering what gearing i should get for better times. Should i stay with the stock gearing or go up a tooth in the front or down. Should i go say 15-43 or 16-44 or maybe 17-44 i dont know, i still want it to be rideable
If I was to guess, i would say slightly lower gearing would give you better times, but as with any kind of racing its trial and error to find your best runs.

I just put the 17/44 set on my 919 and I find it very rideable, even commuting. I would think maybe 16/44 would be the outer limits of shorter gearing and keeping the bike within a reasonable rpm range on the highway.

Btw what kind of times/mph are you running?

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post #3 of 20 Old 07-21-2018, 10:26 AM
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1
I've had 16:45 on for years now.
I did it for track days at our 3500 ft altitude, if at sea level would have used 16:44.
For touring I'd go 17:44 for sure.

2
You'll probably get more time by optimizing your shift points, than a gearing change that is also street practical.

3
Assumed is clutched 1-2 shift and clutchless for the rest.
If you are clutching them all, you'll find yet more time by going clutchless for all but the 1-2 shift.
Do NOT do clutchless 1-2 shifts!

4
Rear tire pressure is a factor.
But I don't know anything about it for drag racing on whatever tire you are using.
Experiment if you already don't have this nailed down.

5
What gear are you trapping in?
That too ought to be a consideration of your sprocket choices.

Between how much better your launch gets better, plus the above, should yield 10ths not 100ths.

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post #4 of 20 Old 07-21-2018, 01:27 PM
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I'm using 15/43 which is perfect for riding around the hinterlands.
I never go on the highway and don't commute.
Try the sprocket calculator to see the effects of different combinations.
Sprocket Calculator - The easy motorcycle sprocket and chain calculator

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post #5 of 20 Old 07-21-2018, 03:45 PM Thread Starter
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Thanks guys, what would be best 16-43 stock gearing or 17-44? And by the way my best time on the 1/8 mile was 7.67 at 98mph

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post #6 of 20 Old 07-21-2018, 04:04 PM
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Originally Posted by Nikolav1990 View Post
Thanks guys, what would be best 16-43 stock gearing or 17-44? And by the way my best time on the 1/8 mile was 7.67 at 98mph
Did you look at the sprocket calculator link I posted?


http://sprocketcalculator.com/

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post #7 of 20 Old 07-21-2018, 04:08 PM Thread Starter
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Yes seems like 17-45 woul be close to 16-43, but im wondering about how the bike feels it is better to go lower on the front sprocket or lower on the rear sprocket.

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post #8 of 20 Old 07-21-2018, 04:17 PM
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The chain has to travel further with a larger rear sprocket, and you will need a longer chain,
so I went with the smaller front one, it slipped straight on and I only needed a small chain adjustment.
Maybe Mcromo44 can chime in to why he went the other way.

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post #9 of 20 Old 07-21-2018, 04:23 PM
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I should add that my chain was almost new when I changed the gearing to 15/43

but the dynamic is huge, my 919 just wants to go now, and accelerates eagerly out of tight corners.
Also much quicker to red line for the odd occasion I find a piece of tarmac long enough.

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post #10 of 20 Old 07-21-2018, 04:24 PM Thread Starter
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Okay so seems like for now i should just stay stock

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post #11 of 20 Old 07-21-2018, 04:28 PM
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There is less stress on the chain with a larger front sprocket, it doesn't have to turn as tight.
I'll mention if you do stick with the stock gearing DID have an endless chain for that. No need for a master link.
Also if you reverse your swing arm pivit bolt you can remove and install a chain intact without taking of the swing arm.

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post #12 of 20 Old 07-21-2018, 04:53 PM
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Quote:
Originally Posted by Nikolav1990 View Post
Okay so seems like for now i should just stay stock
If your chain has a bit of use it's best to do the whole lot together.
As you see, everyone has a preference.
It's true small front sprocket has more stress on it, as it has a tighter turning circle.
I think LDH uses 15/43 for track, maybe he's lurking around here somewhere.

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post #13 of 20 Old 07-21-2018, 06:14 PM
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Quote:
Originally Posted by Diablo View Post
The chain has to travel further with a larger rear sprocket, and you will need a longer chain,
so I went with the smaller front one, it slipped straight on and I only needed a small chain adjustment.
Maybe Mcromo44 can chime in to why he went the other way.
I would not go to 15 teeth for a front.
16s only give 9 effective teeth for power transmission.
A 15 reduces the effective tooth count PLUS reduces the radius of the drive circle thus also increasing chain stress even more.
Why do that for a drag application, which is the worst for shock loads because of the launch of every run, plus the chain spends most of its time seeing higher torque multiplications because it's in the lower gears as compared to the upper gears?
True, a larger rear sprocket will alter the squat/anti-squat relationship and result in less anti-squat, but a rear spring can remedy that.
Just because it's the easiest and cheapest thing to do, does not necessarily make it advantageous in any other way.

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post #14 of 20 Old 07-21-2018, 06:19 PM
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Quote:
Originally Posted by Diablo View Post
I think LDH uses 15/43 for track, maybe he's lurking around here somewhere.

What is the relationship between gearing selection for a road racing circuit that is being tapped out in top gear, and the same bike at a drag strip that never gets past 3rd gear?
Answer: ZERO

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post #15 of 20 Old 07-21-2018, 06:32 PM
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Quote:
Originally Posted by mcromo44 View Post
I would not go to 15 teeth for a front.
16s only give 9 effective teeth for power transmission.
A 15 reduces the effective tooth count PLUS reduces the radius of the drive circle thus also increasing chain stress even more.
Why do that for a drag application, which is the worst for shock loads because of the launch of every run, plus the chain spends most of its time seeing higher torque multiplications because it's in the lower gears as compared to the upper gears?
True, a larger rear sprocket will alter the squat/anti-squat relationship and result in less anti-squat, but a rear spring can remedy that.
Just because it's the easiest and cheapest thing to do, does not necessarily make it advantageous in any other way.
Oh well, I don't care, I like the 15 up front, my chain was too short to add a bigger rear sprocket.
I had the shop fit the new chain and sprockets when they put the new tyres on,
there is no adjustment there to play with, the axle is hard up against the swing arm, and they didn't give me the left over links. I don't ride like a madman, and my chain is a DID 530

So it was either leave it stock or change the front, and I love the way it delivers power now with the 15, it's awesome to ride through the hills, so it's staying on.
My chain was practically new at the time, when I need a new one I'll try a 16/45 with a DID 520

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post #16 of 20 Old 07-21-2018, 06:37 PM
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Quote:
Originally Posted by mcromo44 View Post
What is the relationship between gearing selection for a road racing circuit that is being tapped out in top gear, and the same bike at a drag strip that never gets past 3rd gear?
Answer: ZERO
My bad, I just keep forgetting no ones allowed to have an opinion around here,
no wonder there's so few members.
When you own and run a business, my third successful one, and employ others, and your 60, it's strange to be spoken to like a naughty child.

Enjoy your forum, I have better things to do.

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post #17 of 20 Old 07-21-2018, 06:48 PM
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Quote:
Originally Posted by Nikolav1990 View Post
Okay so seems like for now i should just stay stock
Trapping @ 98 mph on stock OD rear tire and stock gearing translates to being short of ideal RPMs in 3rd gear.
Ideal gearing could be 16:44 or 16:45, definitely not 16/43.
If you gain time early on by technique, a 16:44 appears to be the better at first glance.

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post #18 of 20 Old 07-21-2018, 08:59 PM
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Quote:
Originally Posted by mcromo44 View Post
1
I've had 16:45 on for years now.
I did it for track days at our 3500 ft altitude, if at sea level would have used 16:44.
For touring I'd go 17:44 for sure.

2
You'll probably get more time by optimizing your shift points, than a gearing change that is also street practical.

3
Assumed is clutched 1-2 shift and clutchless for the rest.
If you are clutching them all, you'll find yet more time by going clutchless for all but the 1-2 shift.
Do NOT do clutchless 1-2 shifts!

4
Rear tire pressure is a factor.
But I don't know anything about it for drag racing on whatever tire you are using.
Experiment if you already don't have this nailed down.

5
What gear are you trapping in?
That too ought to be a consideration of your sprocket choices.

Between how much better your launch gets better, plus the above, should yield 10ths not 100ths.
why not clutchless 1-2? ive been doing it the last 46k miles with no problem. its kinda clunky at low speed but i can't imagine doing it any other way when trying to go quickly

also i liked the 17/44 cuz first gear BARELY doesn't lift off on a hard launch, but i haven't tried the 15/46 yet

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post #19 of 20 Old 07-21-2018, 10:02 PM
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Quote:
Originally Posted by nathanktm View Post
why not clutchless 1-2? ive been doing it the last 46k miles with no problem. its kinda clunky at low speed but i can't imagine doing it any other way when trying to go quickly

also i liked the 17/44 cuz first gear BARELY doesn't lift off on a hard launch, but i haven't tried the 15/46 yet
Full power full RPMs clutchless 1-2s?
There's some history saying not to do so, all the way back to the 900RR.
I don't have the particulars, but LDH and some others do.

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post #20 of 20 Old 07-21-2018, 10:47 PM
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Would it have anything to do with occasionally hitting neutral? I know it has happened to me, not in a racing situation, but still.

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post #21 of 20 Old 07-21-2018, 10:54 PM
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Quote:
Originally Posted by mcromo44 View Post
Full power full RPMs clutchless 1-2s?
There's some history saying not to do so, all the way back to the 900RR.
I don't have the particulars, but LDH and some others do.
I mean you just whiff the throttle for a sec and it slips right in. Literally every modern bike with a quickshifter is designed to quickshift from 1st to second at this point and they function by doing exactly the same thing as we do manually. I still thing the honda 919's gearbox is better than even most modern bikes though, so its even easier. Yeah, hitting neutral is much more likely between first and second, but I rarely hit it if i'm making a conscious effort to avoid it.

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post #22 of 20 Old 07-22-2018, 08:22 AM
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Quote:
Originally Posted by Nikolav1990 View Post
Okay so seems like for now i should just stay stock
If you have access to the Dropbox, you might want to check out the Calculators folder.
There are XL worksheets in there for plotting Driving Force curves in order to optimize shift points, as well as gearing X mph.
Keep in mind that the 919 tacho will be over reading significantly at the top of the clock.
If you have a Power Commander you can use a laptop to proof your tach, then make corrections accordingly once you know what the error is.

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post #23 of 20 Old 07-22-2018, 08:24 AM
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Quote:
Originally Posted by nathanktm View Post

also i liked the 17/44 cuz first gear BARELY doesn't lift off on a hard launch, but i haven't tried the 15/46 yet
I'll you'd find a 15/46 quite entertaining!

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post #24 of 20 Old 07-22-2018, 08:26 AM
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Quote:
Originally Posted by mcromo44 View Post
I'll you'd find a 15/46 quite entertaining!
Are those two kits about the same chain length? I'd like a setup where i can just swap out the sprockets without having to worry about chain length when I feel like I want the bike to be a bit more spunky. How can I figure out total chain lengths?

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post #25 of 20 Old 07-22-2018, 08:48 AM
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Quote:
Originally Posted by nathanktm View Post
Are those two kits about the same chain length? I'd like a setup where i can just swap out the sprockets without having to worry about chain length when I feel like I want the bike to be a bit more spunky. How can I figure out total chain lengths?
https://www.rbracing-rsr.com/chainlength.html
I just found the above.
Check it out and play with the numbers.
It looks like the same link count would work for both.
I used an arbitrary centre to centre distance to check, so you'll have to do a proper measurement.

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